(a) Field of the Invention
The invention relates to a method of control of sterilization process, which comprises the steps of measuring the level of degradation of a prion protein degradation indicator when exposed to different sterilization processes.
(b) Description of Prior Art
Biological indicators are considered essential to evaluate the efficacy of any sterilization procedure since chemical and physical monitors are not completely reliable. The latter are useful for detecting gross sterilization, but spore tests are absolutely required for any assurance of sterilization since they are more resistant to heat than viruses and vegetative bacteria. The biological indicators are usually composed of bacterial spores of Bacillus stearothermophilus (for autoclaves and chemical vapor sterilizers) or Bacillus subtilis (for dry heat and ethylene oxide sterilizers) which are removed after sterilization treatment and incubated at the appropriate temperature to observe any microbial growth (Dental Products Report, October 1995, pp. 96-104). However, in this day and age, bacterial spores are no longer the most resistant life forms since the discovery of prions.
Sup35 protein (hereby referred to as Sup35p) carrying [PSI+] is a prion-like protein due to its striking similarities to prions. Indeed, the N-terminal of Sup35p is insoluble in non-ionic detergents and partly resistant to proteases' action. In addition, it principally forms abnormal amyloid filaments composed mainly of β-sheets, as opposed to the normal isoform of the protein mostly formed of α-helices (Glover. J. R., Kowal, A. S., Et al. Cell (1997) 89:811-819; King, C., Tittmann, P. et al. Proc. Natl. Acad. Sci. USA (1997) 94:6618-6622).
The intracellular accumulation of these abnormal prion filaments is responsible for inducing transmissible spongiform encephalopathies in both animals and humans, hence the importance of degrading the filaments in order to prevent any iatrogenic transmission of the disease. Several cases of iatrogenic contamination have been reported due to the utilization of contaminated medical equipment, such as EEG electrodes, which had been previously in contact with Creutzfeld-Jakob patients and inadequately sterilized (Jarvis, W. R. Hospital Infection Control (1985) 12 (12):145-148). Since there also remains the possibility of blood contamination, which has not yet been ruled out, most medical instruments enter in the category of being at risk of being contaminated but that, at different levels depending on the case history of the patient.
The unavailability of sterilization indicators to attest of prion degradation renders the devices inadequate and even dangerous for multiple usage. As of today, most countries have adopted similar requirements for sterilization of contaminated instruments. The recommended procedures for sterilization of medical instruments used on patients at high risk is the incineration of any disposable equipment that has been in contact with a patient or, at the very least, soaking in 1N sodium hydroxide, which is very corrosive for metallic instruments, or autoclaving at 132° C./1 atm pressure for an hour (Rosenberg, R. N. et al., Annals of Neurology (1986) 19(1):75-77; Galtier, F., J. Pharm. Clin. (1994) 13:317-9) which can deform thermosensitive materials such as polymers.
It would be highly desirable to be provided with a novel indicator of prion degradation and therefore, of complete sterilization of medical devices.